An electric wrench of the prior art as disclosed by U.S. Pat. No. 6,477,921 uses a low electric current to drive a driving piece with a side projection to collide with a worm gear so as to activate a sudden movement of the worm gear, whereby a movable jaw will shift on top of a wrench so as to change the clip size of the wrench. It is advantageous to use a lower driving current since the lifespan of the battery can be significantly prolonged. However, there still exist disadvantages of the housing of the motor and the destructive collusion between the worm gear and the driving piece.
The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawings.